Acoustic condenser



May 20, 1930.

P. EL EDELMAN ACOUSTIC CONDENSER Filed April 3, 1929 2 Sheets-Sheet l a0 MNM May 20, 1930. P. E. ED-ELMAN 1,759,809

ACOUISTIC CONDENSER Filed Aplfil 3, 1929 2 Sheets-Sheet 2 Patented May. 20; 1,930

UNITED STATES PATE'r 31u-ICE-y PHILIP E. EDELMA-N, F CHICAGO, ILLINOIS, ASSIGNOR TO,E`CPHRAIM IBANNING, OF

. CHICAGO, ILLINOIS' AcoUsTIc coNnENsER Application 'led April 3, 1929. Serial No. 352,201..I

My present invention relates to an acoustic condenser, and more particularly to improvements in acoustic dielectric type reproducers suitable for talking motion picture or radio use.

An object of the invention is to improve the efficiency and simplify the construction of such apparatus with improved quality,

small bulk, low cost, and life-like reproduction.

A further object is to provide structural improvements. These and other objects as will hereinafter appear are accomplished by this invention, which is fully described in the following specification and shown in the accompanying drawings, in which- Figure 1 is a sectional view of the acoustic condenser combined with a diagram of an operating circuit therefor Y trical diiculties have imposed obstacles to Fig. 2 is a rear view of the acoustic condenser 1 of Fig. v1 drawn upon a reduced scale;

Fig. 3 is a front .view of the acoustic condenser 1 of Fig. 1 also drawn upon a reduced scale* Fig. 4 is a rear view of a modification of Fig. 2;

Fig. 5 is a plan view of a segment of screen electrode 3 of Fig. 1; and

Fig. 6 is a plan view of a modified construction of said screen electrode.

Acoustic condensers have long been known 1n the art, but various mechanlcal and electheir satisfactory public use. It is desirable to have an adjustable means as provided in this invention for tensioning the operative diaphragm to obtain'uniformly good reproduct-ion therefrom. y

Reference is now made to Fig. 1, in which the numeral 1 indicates a sectional `view of the acoustic condenser. Itcomprises a frame of wood or other suitable material. Frame 2 preferably has a channel portion 51 formed therein. An electrode 3, preferably consistingFof a flexible screen composition, as shown in 4ig. 6, may be prepared by pasting ribbon strips of metal foil 56, 56, 56, etc., about l to 1/ wide with electrically conductive adhesive cement on a fabric sheet 62, composed ldielectric constant for the of suitable air permeable material, such as canvas, aeroplane cloth or metal cloth. The.

ribbon foil strips 56, 56, etc., are spaced from each other at a distance not greater than one half of the width thereof.

Similar metal foil strips 57, 57, 57, etc., are crosswise cemented to Hexible fabric 62,- thereby'forming portions 59, 59, 59, etc., oh the surface of fabric 62 which are not covered by the aforesaid metal foil ribbons. Any suitable electrically conductive cement may be used to fasten the strips 56, 56 and 57, 57, etc., on fabric 62. A contactor strip of metal foil 60, and a similar strip 61 are placed over the ends of ribbon foil strips 56, 56 and 57, 57, etc., respectively to electrically join all of the strips 56, 56, 57,57, etc. i

, Such shown in Fig. 6, affords the necessary properties, but any equivalent structure of similar characteristics affording a flexible screen'electrode material for screen electrode 8 may be used. Thus, either the aforesaid material shown in Fig. 6, or else a flexible wire screen,

or a woven metal cloth, or wire or metal ribbon Woven material is stretched over frame 2 as shown, vand fastened thereto by means of fasteners, such as tacks 8. Any suitable fastening means may be used for this purpose, preferably drawing the edge of screen eleca screen electrode 3 prepared, as

trode 3 into channel 5l offrame 2. Screen electrode 3 may have meshes proportioned from 8 to 200 or more per inch, as shown in Fig. 5, and has a small stud 4 fastened thereto, preferably by solder 5 located preferably at a central portion of the surface thereof.

Stud 4 has an indented portion 6 adapted to lfit one end of an adjusting screw 7.

Stretched over screen electrode 3 is a dielecas empire cloth, cfharacterized by high dielec-` tric strength, durable flexibility, and good purpose. Rubberized silk fabric is also suitable. Dielectric sheet 9 is prepared with an adherent thin electrode coating 10 on one surface thereof,

.sheet with its adherent electrodei and is stretched therewith and fastened to f frame 2 'by vfasteners 11, 12, so that sufficient fastener tacks 12, for example, hold dlelectrlc around frame 2.

Dielectric sheet 9 and its electrode coating 10 is thereby caused to be positioned adjacent to screen electrode 3, butfree'V to move withl respect thereto. Screen 'electrode 3 affords sufficient air passages to permlt the free movement of dielectric sheet 9 with its. electrode coating 10.

The electrode .coating 10 of dielectric sheet 9 may be embossed thereon with metal leaf in the same manner that book covers are gold-stamped, and may be'applied '1n any suitable manner and consists of any suitable sheet 9 by well known methods as used in the art of galvanoplasty, such for example as set forth in the standard textbook Electro- Deposition of Metals by Langbein; Henry 4Carey Baird & Co., publishers, New York, 1924, chapter 17. Only one side or surface of dielectric sheet 9 is coated with conductor electrode metal 10. The thickness of electrode metal 10 may be built up to any desired thin dimension by subsequent electroplating. as set forth in the aforesaid textbook, and in such thinness vwill withstand strains incidentto use of the dielectric sheet 9. Dielectric coating 10 is effectively insulated from electrode screen 3 as shown, and a terminal may be taken therefrom through a washer 13. Washer 13 is held against a portion of coating 10 by screw 11, and wire 21 is soldered thereto at 14.I

The backiofframe 2 carries a spider or support member 15, fastened thereto by fasteners, such as screws 16. A threaded bushing 17 is centrally carried' by support 15 suitably fastened thereto by rivets 18. A terminal wire 2O is soldered to one of the rivets'18 through a. lug 19. Adjusting screw 7 is 'carried by threaded lug 17, and is provided with aknob fastened to screw 7 at 2 3. Support member 15 only extends over a small portion of the rear/end of frame 2.

Upon first assembly-of the aforesaid elements, the electrode 3, the dielectric sheet 9, and the electrodecoating 10 on sheet 9 will be substantially fiat, stretched and supported on frame 2." It has heretofore been difficult to obtain a satisfactory closely spaced relation of the electrodes and ldielectric sheet in such apparatus andto maintain same, due to 1,0 lfirmly. eflicient relation initially land thereafter.

ythe fact that one thereof tends to become loose with respect to the other.

rovide adJusting means to maintain the I working electrodes and dielectric sheet in Screw'? may be turned in its threaded sup- 'port 17 to push metal stud 4 to stretch screen electrode 3 outwardly from the plane of .frame 2. At the same time, dielectric sheet 10 with its carried electrode coating 10 ill ,be similarly pushed outwardly, as shown 1n Fig.

1. The tensioning may be adjusted empirically for best results, and may at any future time be altered when necessaryor desired by means of screw 7.

This means also causes a thin layer of air to intervene between dielectric sheet 9 and screen electrode 3, electrically variedin the A manner presently to be set forth. Sheet 9 with its carried. electrodecoating 10 is free to move with respect to electrode 3, and this structure affords an eliicient combination having a high percentage ofvworking area. The

woven or screen structure afforded by woven metal wire or r1bbon used for electrode 3,

contact areas to be afforded thereby to cocauses a large number of depressed and raised v bly supported adjacent thereto. Electrode metal 10 being fastened to dielectric sheet 9, causes -sameio move under the iniuence of electrical forces applied thereto, and such electrical forces arethereby utilized at im'- proved eiciency. f

An exemplification of a suitable operating ioo circuit for the acoustic condenser will now be described with reference to Fig. 1.' Terminal wires 20-and 21 of the acoustic condenser 1 connect to a high voltage condenser 24, of 1 mfd. size. This condenser 24 readily passes fluctuating or alternating currents om the' output of amplifier vacuum tube 25, and also serves as a source of polarizing direct current potential supplied to condenser 24 through resistances "41T, 40-of` about 250,000 ohms each, from rectifervacuum tube 35 and transformer 34. i'

A direct current potential of the order yof 500 volts may thereby be maintained across terminals 20, 21 of the acoustic condenser 1 by condenser 24. Vacuum tube 35 may be an ordinary radio amplifier tube having its gridV 37 and plate'38 connected together at termi'- nal 39, connected to resistance40. Filament 36 of vvacuum tube 35 is supplied with energizing current by winding 43 of transformer 34. The necessary high voltage alternating current to be rectified by vacuum tube 35 is supplied by winding 42 of small transformer 34. The primary 44 of transformer 34 connects the plug connector 31 through wires 32, 33, to which a source of alternatingcurrent may be supplied.

A switch"52 serves to control all of the alternating current supplied through a plug connector 31. A power supply unit 30 also is operated through a plug 31 and switch 52 to afford operating filament and plate current for vacuum tubes, kwhich may be used in connection with acoustic condenser 1, as indicated by Vacuum tubeapparatus 29 and Vacuum tube 25. Vacuum tube apparatusv 29 may comprise any radio set or amplifier or talking motion picture amplifier having audio output terminals 45. Terminals 45 connect to input termin-als 46 of amplifier vacuum tube 25. A small condenser 49 of 1/2 mfd. capacity by-passes thegrid bias potential operating grid 27 from power unit 30.

` Plate current issup-plied to vacuum tube 25 from power unit 30 by terminals 48, 47 thereof, through a choke coil 26 whereby the potential available from terminals 47, 48 is also utilized additive to the potential avail. able from terminals of condenser 24 as aforesaid, to polarize the eleetrodes 10 and 3 of acoustic condenser 1,` with a direct current potential combined from said two sources of polarizing potential, namely terminals 47, 48 of power unit 30, plus the potential maintained at condenser 24, through Aresistances 40, 41, as aforesaid.

The audio input to vacuum tube 25 is thereby amplified by vacuum tube 25 -so that the amplified output potential from vacuum tube 25 is impressed upon the acoustic condenser electrodes 10 and 3 through wires 54, connecting to wire 21 and 53, connecting to condenser 24, to which latter wire 20 is connected.

The audio output of vacuum tube l25 is thereby -impressed on acoustic condenser 1 simultaneously with the polarizing or operating direct current potential, as set forth. The output potential from vacunm'tube 25 so impressed upo'n condenser reproducer 1, should be of the order of` 20% or less of the direct current polarizing potential simultaneously impressed thereon. From Fig. 2 it will be evident that the support member 15 carried by frame 2, offers no substantial resistance to the free propagation of sound waves from the acoustic condenser 1. As sh wnVA in Fig. 3, a series of pleat-like wrinkles? 50 may slightly form on electrode coating 10 when same is pushed outwardly from the plane of frame `2, astdescribed in Fig. 1. Such small wrinkles are beneficial to j the result as the dielectric sheet 9 is similarly wrinkled in such case, affording slight air passages between dielectric sheet 9 and electrode screen 3, of Fig. 1. 1

The shape. of the frame 2 is immaterial, and may for example besquare or rectangular, oval, or circular, but the area of screen electrode 3 should preferably be not less than 340 square inches. It may be larger or smaller .than this, and if smaller', a plurality of duplicate acoustic condensersof such smaller area may bey used, connected in parallel. If

desired, the acousticcondenser may be arranged as in Fig. 4, with a circular shaped frame 2 provided with three support members 15 to hold lug 17. A baille .plate 55 may be provided for frame 2, asis customary in the art. A suitable construction for the Woven material of screen 3 is shown in Fig. 5. Ribbons 56 interweave with ribbons 57 to form air spaces 59.

While I have shown and described but a few embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the constructionfand arrangement may be made which do'not depart from the spirit and scope of the invention as disclosed in the appended claims. v

I claim: 1. An acoustic condenser comprising, in combination, a supporting frame, a flexible woven screen electrode carried thereby, a dielectric sheet supported adjacent to said electrode, and an velectrode carried by said dielectric sheet. v

2. A condenser reproducer comprising, in

combination, a supporting frame, a flexible woven screen electrode carried thereby,l a cooperating dielectric sheet adjacent to said electrode, and a conducting coating supported on said dielectric sheet.

3. A condenser reproducer comprising, in combination, a stretched flexible perforate electrode, a flexible dielectric diaphragm held adjacent thereto, an electrode secured on said dielectric diaphragm, and adjusting means for tensioning one of said electrodes.

4. A'condenser reproducer comprising, in combinationa stretched flexible screen electrode, a dielectric sheet held stretched adjacent thereto, a conductive electrode secured on said dielectric sheet, and means to adjust the position of said screen electrode with respect to said dielectric sheet.

5. A condenser reproducer comprising, in combination, a frame, a flexible Woven metal electrode supported-thereon, a dielectric diaphragm fastened to said frame and stretched adjacent to said electrode, aco-operating electrode coating carried by said diaphragm, and means carried by said frame to adjust the operative contour of said electrodes and diaphragm.

6. An acoustic condenser for reproducing sound waves comprising, in combmation, a frame, a pair of flexible electrodes separated by a dielectric sheet and carried by saidl frame, means to stretch one'of said flexible electrodes, and an operating circuit connected to said electrodes.

7. A condenser reproducer consisting of,

in combination, a frame, a flexible electrode stretched thereon, a co-operating flexible dii electric sheet held adjacent to said electrode,

8. An acoustic condenser comprising two electrodes separated by a dielectric, one of said electrodes comprising a flexible metal l cloth having spaced metal strips secured thereon;

9. An acoustic condenser comprising two electrodes separated by a dielectric, one of said electrodes comprising a flexible metal cloth having spaced metal strips secured thereon, some of said strips extending transversely of the metal threads of the metal i cloth so as to make electrical contact therewith.

10. An acoustic condenser comprising two electrodes separated by a dielectric, one of said electrodes comprising a' exible metal cloth having spaced metal strips secured thereon, and means for tensioning said metal cloth electrode.

11. A condenser reproducer comprising in combination, a stretched flexible perforate electrode, a flexible dielectric diaphragm held adjacent thereto, an electrode secured on said. dielectric diaphragm, and adjusting means for tensioning'both of said electrodes.

In testimony whereof, I have hereunto set my hand this 29th day of March, 1929.

PHILIP E. EDELMAN. 

